A coating type magnetic recording medium which is prepared by dispersing a magnetic oxide powder such as .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, a berthollide compound of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, Co-doped berthollide compound of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, Co-doped berthollide compound and CrO.sub.2 or an alloy magnetic powder mainly composed of Fe, Co or Ni in an organic binder such as vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, epoxy resin or polyurethane resin, coating and drying it has been widely used.
There has been an increase in the demand for high density recording. Accordingly, attention has been given to so-called non-binder type magnetic recording media using a ferromagnetic thin metallic layer formed by a vacuum evaporation method, a sputtering method or an ion plating method without a binder. Various attempts have been made to produce this type of recording media.
It is desirable for a magnetic recording medium which comprises providing a ferromagnetic metallic thin layer on a plastic film such as a polyester film to be capable of higher density recording. Accordingly, skew caused by a dimensional change of the magnetic recording medium must be substantially prevented. However, present non-binder type magnetic recording media have not been able to eliminate enough of the skew.
When a metallic thin layer is provided on a plastic film such as a polyester film, curing of the magnetic recording medium readily occurs. This causes running problems or causes an intermittent contact with the magnetic head in the magnetic recording device. A heat treatment as disclosed in Japanese Patent Publication No. 12420/60 is conducted to remove the above referred to curling. However, the heat treatment is not capable of improving skew in the magnetic recording medium having a ferromagnetic metallic thin layer prepared by a vapour deposition method or a plating method.